Animal skin serves essential roles in protecting an organism from environmental insults. Numerous specific skin functions include protection, excretion, secretion, absorption, thermoregulation, pigmentogenesis, accumulation, sensory perception, and regulation of immunological processes. The structural and chemical changes in the skin during aging reduce the effectiveness of skin to achieve each of these principal functions. Upon reaching the later stages of life, most previously robust skin functions are reduced, some by as much as 50-60%. The physiological changes associated with these reductions include impairment of the barrier function, decreased turnover of epidermal cells, reduced numbers of keratinocytes and fibroblasts, and a reduced vascular network particularly around hair bulbs and glands. A side effect of these changes is an increase in the appearance of skin wrinkles and previously unrecognized pigmented areas.
In an effort to prevent unwanted aging of skin or the appearance of aged skin, many people use chemical peels to reduce wrinkles and increase skin cell renewal. Normal skin represents a balanced cell renewal system where fully differentiated corneocytes are continually shed and replaced by new cells generated at lower skin levels. Normally this process occurs at a steady state whereby the new cells are produced at rates equivalent to the shedding of surface cells. Chemical peels offer a way to increase this rate of skin renewal. Peels function by actively removing damaged outer layers of skin, replacing it with new, more hydrated, and more robust skin cells. This improves the smoothness of skin, reducing wrinkles, and providing a younger appearance. Chemical peels are also beneficial for those with facial blemishes such as acne scarring, anomalous pigmentations, or for removing actinic keratoses.
Chemical peels are available in several formulations that provide superficial, moderate, or deep peels. Irritancy is a hallmark of all chemical peels, and all peels induce irritancy in the skin of a subject, even superficial peels. Traditionally, this irritancy is a source of the peeling nature of the compositions.
Superficial chemical peels typically remove only the upper corneous layer of the epidermis. Peeling agents include alpha-hydroxy acids including citric acid (e.g. citrus-derived), glycolic (derived from sugar cane), lactic acid (derived from milk), malic acid (derived from apples) and tartaric acid (derived from grapes). These are the mildest of agents yet produce extreme irritancy such as stinging, redness, dryness, and other skin irritation. Typically only mild skin smoothing or acne improvements are observed with this level of chemical peel.
Moderate depth chemical peels penetrate into the upper layers of the dermis causing more aggressing sloughing of the outer skin cell layers. Typical agents for moderate peels include higher concentration hydroxy acids and trichloroacetic acid at concentrations of 20-50%. The greater the concentration of the peeling agent, the deeper the peel. Moderate peels function to smooth fine surface wrinkles, surface blemishes to the skin, and unwanted pigmentation. The irritation to the skin is much greater than a superficial peel and recovery times and precautions are also increased.
The deep peel, commonly achieved by applications of phenol, is used to treat deep wrinkling, remove deeper pigmentation anomalies, and treat precancerous skin growths. Phenol peels contain highly irritating ingredients that can have long lasting affects on skin appearance. Phenol peels can leave the skin with a lighter pigmentation and damage the skin cells such that new pigment production cannot occur. Recovery from phenol peels can be several months and may require permanent avoidance of sun exposure.
The ubiquitous irritating nature of prior skin renewal enhancing compositions is inherent to the compositions, previously thought essential for function and the primary source of unwanted side effects of treatment. Thus, there exists a need for compositions, systems, and methods of enhancing skin renewal while reducing irritancy.